There are many occasions where the torque to be applied to a rotational workpiece must be measured with a high degree of precision. A common example is a machine assembly where the members must be joined and fastener together securely, but with a limited amount of stress between one another.
Devices have been designed to measure torque on a rotational workpiece. Generally, they all have a head suited to rotate coaxially and in cooperation with the workpiece and a lever arm extending from the head and perpendicular to the axis of rotation for reacting to forces acting at a distance from the head.
In the cases where the actuating force that produces torque is applied to the lever arm, the device acts as a torque wrench. Torque is then determined through measuring the resultant elastic strain in the lever arm. Alternatively, the device may operate passively, where in contrast to the wrench, the torque actuating force is not applied directly to the device. In this instance, as the device rotates the lever arm encounters a reactionary force, often a spring loaded stop, which causes elastic strain in the arm. Again, the torque is determined through measuring these strains.
One of the major design difficulties has been to develop an apparatus that will give an accurate measurement of torque irrespective of the point of force application on the lever arm. Prior art solutions to this problem have involved the use of strain transducers, typically strain gages, placed on the lever arm at selected points to sample the elastic strain and to determine therefrom the torque existing at the axis of rotation. The transducers are usually arranged in one or more bridge circuits, the outputs of which are related to the applied torque. The bridges necessary to provide the desired output have been of relatively sophisticated design, requiring groups of eight or more transducers. This high level of complexity has reflected itself in increased cost, maintenance and quality control problems.
Thus, it has become desirable to develop an improved torque measuring device of simpler design, but yet without sacrificing accuracy. Such is the objective of the present invention.